After the administration of cytostatic drugs, an increase in thromboembolic phenomena has been described in cancer patients. The authors studied the changes in plasmatic coagulation and fibrinolysis in 40 patients with nonoperable Stage III and IV lung cancer after cytostatic chemotherapy. The results show significant postchemotherapy increases in fibrinopeptide A levels, as well as a decrease in fibrinolytic activity reflected by a drop in functional tissue activator. Also the authors studied the potential accumulative effect of three chemotherapy cycles. A significant increase in functional plasminogen activator inhibitor has been noted. Chemotherapy is apparently capable of conditioning a decrease in fibrinolytic activity in these cancer patients that could be related to the enhanced tendency to developing thromboembolic phenomena after cytostatic chemotherapy.